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Question

Simplify: $3((\frac{5}{3})x^2 - 28x + 15) - 5(x^2 + 6x - 15)$

This question was previously asked in
RRB NTPC 2024 CBT 1 Question Paper (28-Aug-2025) (Shift 3)
The correct answer is
$-114x + 120$

Algebraic Expression Simplification

The goal is to simplify the given algebraic expression:

$3\left(\left(\frac{5}{3}\right)x^2 - 28x + 15\right) - 5(x^2 + 6x - 15)$

Step 1: Distribute the First Constant

Multiply the terms inside the first parenthesis by 3:

  • $3 \times \left(\frac{5}{3}\right)x^2 = 5x^2$
  • $3 \times (-28x) = -84x$
  • $3 \times 15 = 45$

The first part becomes: $5x^2 - 84x + 45$

Step 2: Distribute the Second Constant

Multiply the terms inside the second parenthesis by -5:

  • $-5 \times x^2 = -5x^2$
  • $-5 \times (6x) = -30x$
  • $-5 \times (-15) = 75$

The second part becomes: $-5x^2 - 30x + 75$

Step 3: Combine Like Terms

Combine the results from Step 1 and Step 2:

$(5x^2 - 84x + 45) + (-5x^2 - 30x + 75)$

Group like terms:

  • $x^2$ terms: $5x^2 - 5x^2 = 0$
  • $x$ terms: $-84x - 30x = -114x$
  • Constant terms: $45 + 75 = 120$

The simplified expression is $-114x + 120$.

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